The present invention relates to an antenna device and a mobile terminal and more particularly to an antenna device contained in a mobile phone and a mobile phone using the antenna device.
Antennas contained in housings of mobile phones are conventionally known as receiving/transmitting antennas for the mobile phones.
These antennas are classified into linear antennas and plate antennas depending on their characteristics.
FIG. 20 is a schematic plan view of a mobile phone containing a dipole antenna that is one of conventional linear antennas. Referring to FIG. 20, a conventional mobile phone 1x has a housing 10 and an antenna device 3x accommodated in housing 10. Antenna device 3x has a substrate 11 and a dipole antenna 121 provided on substrate 11. Dipole antenna 121 has two meander-like antenna portions 121a and 121b respectively connected to a feed point 12. The electrical length of dipole antenna 121 is xcex/2.
During a call, the direction in which such a dipole antenna 121 extends (the direction indicated by an arrow 125) is approximately at a 30xc2x0 angle with respect to a vertical direction. Therefore, dipole antenna 121 is known as an antenna which allows for reduction of polarization loss for a wave polarized vertically to the ground (a vertically polarized wave) at the time of a call.
FIG. 21 is a diagram showing a radiation pattern of the conventional dipole antenna shown in FIG. 20. As shown in FIG. 21, when mobile phone 1x is placed upright, particularly when the electrical length of the antenna is xcex/2xc3x97A (A is an integer), a null point 134 of the radiation pattern as indicated by solid lines 131 and 132 is in a horizontal plane. This disadvantageously reduces the gain.
FIG. 22 is a graph showing the relation between the electrical length of the antenna and the current distribution on the antenna element in the conventional dipole antenna. As shown in FIG. 22, in the dipole antenna having an electrical length of xcex/2, the maximum value of the current distribution exists at the portion where the electrical length of the antenna is xcex/4, that is, at the central portion of the antenna. As a hand easily touches this portion, an antenna gain degrades particularly when a hand touches it.
FIG. 23 is a plan view of a mobile phone having a conventional plate antenna. Referring to FIG. 23, a mobile phone 1y has a housing 10 and an antenna device 3y accommodated in housing 10. Antenna device 3y has a substrate 11 and a plate antenna 122 provided on substrate 11. Plate antenna 122 is connected to a feed point 12.
Such a plate antenna 122 easily receives and transmits both a vertically polarized wave and a horizontally polarized wave with respect to the ground. Advantageously, degradation amount of gains when a finger touches the antenna is small as compared with a linear antenna, since the current in the vicinity of the feed point is dispersed.
Plate antenna 122, however, for example a patch antenna, requires about xcex as the total perimeter of the antenna, the size of the antenna inevitably increases and thus mobile phone 1y itself increases in size.
The present invention is therefore made to solve the above problems. An object of the present invention is to provide an antenna device capable of receiving and transmitting both a vertically polarized wave and a horizontally polarized wave, being reduced in size and having small gain degradation during a call.
An antenna device in accordance with the present invention includes a substrate and an antenna provided on the substrate and having an electrical length of approximately (xcex/2)xc3x97A (A is an integer). The antenna includes a plate antenna portion positioned at a portion where an electrical length from an end portion is approximately xcex/4+(xcex/2)xc3x97B (B is an integer), and a linear antenna portion connected to the plate antenna.
In the antenna device thus configured, the linear antenna portion can mainly receive and transmit either one of a vertically polarized wave or a horizontally polarized wave, and the plate antenna portion can receive and transmit both the vertically polarized wave and the horizontally polarized wave. As a result, both the vertically polarized wave and the horizontally polarized wave can be received and transmitted, resulting in a high gain antenna.
Furthermore, since the electrical length of the antenna is approximately (xcex/2)xc3x97A (A is an integer), the current is large at the portion where the electrical length from the end portion of the antenna is approximately xcex/4+(xcex/2)xc3x97B (B is an integer). However, this portion is provided with the plate antenna portion and therefore the current can be distributed. Accordingly, even when a finger is placed on this portion, degradation in gain can be reduced.
Furthermore, since the antenna includes the linear antenna portion, the antenna can be reduced in size as compared with an antenna configured only with a plate antenna portion.
More specifically, the present invention can provide an antenna having a high gain even at the time of a call, assuring a gain when the terminal is placed upright, and having a small size.
Preferably, the linear antenna portion includes at least one selected from the group consisting of a monopole antenna, a zigzag antenna, a meander line antenna and a helical antenna.
More preferably, the substrate has a main surface having conductivity. The antenna further includes a connection portion connected to the main surface of the substrate. In this case, since the antenna is connected to the main surface having conductivity, an image is formed on the substrate. As a result, the electrical length of the antenna is approximately double the physical length of the antenna, so that the physical length of the antenna can be shortened. Therefore, the antenna device can be reduced in size.
Preferably, the substrate has a main surface and a side surface continuous with the main surface, and the antenna is provided on the side surface. In this case, since the main surface is not provided with an antenna, other device and the like can be placed on the main surface.
A mobile terminal in accordance with the present invention includes a housing and an antenna device contained in the housing. The antenna device includes a substrate and an antenna provided on the substrate and having an electrical length of approximately (xcex/2)xc3x97A (A is an integer). The antenna includes a plate antenna portion positioned at a portion where an electrical length from an end portion is approximately xcex/4+(xcex/2)xc3x97B (B is an integer), and a linear antenna portion connected to the plate antenna portion.
In the mobile terminal thus configured, the linear antenna portion can mainly receive and transmit either one of a vertically polarized wave or a horizontally polarized wave and a plate antenna portion can receive and transmit both the horizontally polarized wave and the vertically polarized wave. As a result, both the vertically polarized wave and the horizontally polarized wave can be received and transmitted, resulting in a mobile terminal having a high gain antenna device.
Furthermore, since the electrical length of the antenna is approximately (xcex/2)xc3x97A (A is an integer), the current is large at the portion where the electrical length from the end portion of the antenna is approximately xcex/4+(xcex/2)xc3x97B (B is an integer). However, since this portion is provided with the plate antenna portion, the current can be dispersed. Therefore, even when a finger or the like is placed on this portion, degradation in gain can be reduced.
Furthermore, the antenna includes the linear antenna portion, and thus the antenna and the mobile terminal can be reduced in size as compared with an antenna configured only with a plate antenna portion.
In addition, since the antenna device is contained in the housing, the antenna device is less affected by a human body. As a result, degradation in gain can be prevented.